1. Field of the Invention
The present invention relates generally to prosthetic implants and pertains, more specifically, to a construction and a method for facilitating securement of a selected augment to an implant component, such as the securement of a selected tibial augment to a tibial implant component of a prosthetic knee implant.
2. Description of Related Art
In a knee implant procedure, for example, very often tibial augments, or spacers, are employed by a surgeon to compensate for a bone defect encountered at the implant site. Typically, a tibial augment is selected during the course of surgery, upon observation of the actual implant site, and is attached by the surgeon to the lower, or distal surface of the tibial tray of a tibial implant component utilizing attachment screws, bone cement, or a combination of screws and cement. Both screws and cement exhibit certain drawbacks.
Thus, where bone cement is used to attach a tibial augment to the tibial tray, the cement ordinarily is mixed during surgery and is placed between the augment and the tibial tray. The tibial augment then is secured in place with a clamp and is held in place until the cement cures. Unwanted delay is experienced as a result of the requirement for waiting until the cement cures before going forward with the implant procedure. In addition, the extra steps involved in mixing the cement, applying the cement, and then clamping the augment to the tibial tray require added effort as well as increased time, all to the detriment of both the patient and the surgeon.
The use of attachment screws requires the mechanical assembly of a selected tibial augment with the tibial tray of a tibial implant component, again during surgery. The tibial tray is provided with apertures passing entirely through the tibial tray, and the tibial augment includes holes in locations corresponding to the apertures in the tibial tray. In executing the assembly, screws either are inserted through unthreaded apertures in the tibial tray and then threaded into corresponding threaded holes in the tibial augment to secure the augment against the distal surface of the tibial tray, or the screws are passed through unthreaded holes in the augment to be threaded into threaded apertures in the tibial tray to secure the augment in place. In either procedure, the surgeon must contend with handling small loose screws and threading the screws into place. In addition, apertures in the tibial tray can allow particulate polyethylene debris from a bearing member supported at the proximal surface of the tibial tray to migrate through the tibial tray and into the adjacent bone during service of the implant, causing deleterious effects. Further, the presence of apertures in the tibial tray reduces the area of the proximal surface available for support of the bearing member, thereby increasing stress on the material of the bearing member and encouraging cold flow of polyethylene into the apertures of the tibial tray, with concomitant distortion of the bearing member.